Fertilization in brown algae. II. Evidence for lectin-sensitive complementary receptors involved in gamete recognition in Fucus serratus.

Fertilization in Fucus serratus is directly proportional to the number of sperm added, saturating at approximately 250 sperm per egg with an apparent Km of 120 sperm per egg. The effect of a range of lectins on fertilization has been tested. Preincubation of gametes with Con A and fucose-binding protein (FBP) inhibited fertilization. At low concentrations this was by specifically binding to eggs; at high concentrations pretreatment of either gametes inhibited fertilization probably due to cytotoxicity. Fertilization was not inhibited by simple sugar haptens, but polysaccharides containing fucosyl or mannosyl residues (yeast mannan, fucoidan, ascophyllan) inhibited fertilization by binding to sperm. Pretreatment of eggs with alpha-fucosidase or alpha-mannosidase was effective in inhibiting fertilization. All the results indirectly demonstrate that fertilization in Fucus serratus is based on an association between fucosyl- and mannosyl-containing ligands on the egg surface and specific carbohydrate-binding receptors on the sperm surface.